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Recommended 3.3V to 5V and 5V to 3.3V I2C Level Shift Solution

Jim CHEN
Expert 4795 points
Other Parts Discussed in Thread: ISO1540, P82B715

Dear Team,

My customer is looking for a 5V to 3.3V I2C Level shift that connect between J4 and J2 in figure1, and one 3.3V to 5V I2C level shift that connect between J3 and J2 in figure2.

Could you help to find the solutions for my customer? 

Thank you.

Figure 1:

  • 0
    TI__Guru 61830 points

    Jim,

    The diagram you provided does not show the cable extender device (P82B715) being used properly and does not provide what side is connected on the ISO1540 (side 1 and side2).

    P82B715 is already a level shifter device but requires both cable sides be connected via P82B715. The ISO1540 requires a 'true buffer' on its offset side because it does not support more than 40pF of capacitance whereas the P82B715 is not a true buffer and will not isolate the bus capacitance.

    How exactly are these boards connected and do you really need the isolation feature that ISO1540 offers?

    -Bobby

  • 0 in reply to BOBBY
    TI__Expert 4795 points

    Hi Bobby,

    I just send the schematic to you and your team for reference. Their P82B715 is NXP solution not TI solution. 

    https://www.nxp.com/docs/en/data-sheet/P82B715.pdf

    My customer's schematic cannot modify anymore, but they want to add one 5V to 3.3V level shift between J4 and J2 in figure 1 and add one 3.3V to 5V level shift between J3 and J2 in figure 2, is it possible?

    Thank you.

    Regards,

    Jim

  • 0 in reply to Jim CHEN
    TI__Guru 61830 points

    Jim,

    I replied to your email. I believe we can continue the discussion offline.

    -Bobby